Air Navigation: VFR, Pilotage, and Radio Navigation

• Navigation is the method to determine position, course, and distance travelled

Navigation Breakdown

• Where you are

• Where you want to go

• The route to your destination

• How much time and fuel it requires

• Air navigation is determining the position of an aircraft with respect to the Earth's surface and maintaining course

Visual Flight Rules (VFR)

• VFR govern aircraft operation in Visual Meteorological Conditions (VMC)
• Flight is possible by visual reference under VFR
• VFR aircraft may have limitations in controlled airspace because of limited communication/navigation equipment

Pilotage

• Pilotage uses fixed visual ground references to guide oneself to a destination
• A map or aeronautical chart may be used
• It involves identifying present position and direction of flight by visual contact with terrain
• Examples of visual references include Mt Arayat and Mayon Volcano

Radio Navigation

• Radio Navigation is navigating or piloting an aircraft using instruments and navigational systems only
• Navigational systems include VHF Omni directional Range (VOR) and Automatic Direction Finder (ADF)

Instrument Flight Rules (IFR)

• IFR is a set of regulations dictating how aircraft operate when pilots cannot navigate using visual references under visual flight rules
• Aircraft must have instrumentation and be certified by regulatory authority for instrument meteorological conditions (IMC)
• Pilots in IMC must hold an instrument rating.

Automatic Direction Finder (ADF)

• Automatic direction finding (ADF) is an electronic aid that identifies an aircraft's relative bearing from a radio beacon
• Radio beacons transmit in the MF or LF bandwidth, such as a Non-Directional Beacon
• ADF is the oldest navigational system in use
• ADF receives radio signals from ground facilities called Non-directional Beacons (NDB)
• ADF can receive commercial broadcasting stations operating from 415-1750 KHz

Non-Directional Beacon (NDB)

• Ground-based radio transmitter that transmits radio energy in all directions
• NDB operates at a frequency between 190-415 KHz LF and 510-535 KHz MF
• NDB has a limited operating range
• Weather strongly affects NDBs
• NDBs are used by Automatic Direction Finder (ADF) equipment

ADF / NDB Airborne Equipment

• Consists of ADF Antenna, ADF Receiver, ADF Indicator
• The ADF Antenna consists of:
  • Directional antenna
  • Sense antenna

Definition of Terms

• Magnetic Heading (MH) is the direction the aircraft's nose is pointed
• Relative Bearing (RB) is the degrees from the nose of the aircraft to the transmitter, measured clockwise
• Magnetic Bearing to/from (MBTO / MBFROM) is the direction to be flown to or from the station

Types of ADF Indicator

• Fixed Card ADF
• Movable Card ADF

Fixed Card ADF

• Always shows 0 degrees at the top
• The needle always shows Relative Bearing (RB)

Movable Card ADF

• Manually adjusted to show magnetic heading at the top
• The needle always points to Magnetic Bearing to the station (MBTO)

Very High Frequency Omni Directional Range (VOR)

• VHF Omnidirectional Radio Range (VOR) is an aircraft navigation system operating in the VHF band
• VORs broadcast a VHF radio composite signal that includes a station's Morse Code identifier
• The receiver can use the signal to derive the magnetic bearing from the station to the aircraft, known as the "radial"
• This is the most widely used method of radio navigation
• Operates on Frequencies 108-117.95 MHz
• VORs are accurate to within +/- 1 degree.
• They automatically compensate for wind drift.

Principles of Operation

• VOR stations transmit radio beams, called radials, outward in every direction, based on Magnetic North

VOR Station

• VOR stations have a limited range of 200 miles due to the signals being line of sight
• Each station broadcasts a VHF radio composite signal that includes a navigation signal, station's identifier, and voice
• The navigation signal allows receiving equipment to determine a bearing from the station to the aircraft in relation to Magnetic North
• The station's identifier is typically a three-letter string in Morse code

How does the VOR station work?

• The VOR station uses Reference and Variable phase

Classes of VOR

• Terminal VOR
• Low Altitude VOR
• High Altitude VOR

Terminal VOR

• A low-powered VHF Omnidirectional Radio Range located at or near an airport for final approach clearance
• TVOR has a range of 25 NM from 1,000 feet AGL to 12,000 feet AGL

Low Altitude VOR

• Low-altitude VORs are to be used from 1,000 feet AGL through 18,000 feet AGL at distances of up to 40 NM from the station

High Altitude VOR

• High Altitude VOR (HVOR) service volumes vary based on altitude
  • 1,000 feet AGL up to 14,500 feet AGL range: 40NM
  • 14,500 feet AGL up to 18,000 feet range: 100NM
  • 18,000 feet up to 45,000 feet range: 130NM
  • Over 45,000 feet range: 100NM up to 60,000

VOR Airborne Equipment

• Consists of an Antenna, VHF/NAV Receiver, and Indicator

VOR Limitations

• Line of Sight: Terrain obstructs VOR
• Cone of Confusion: Occurs near the VOR station where the CDI needle becomes erratic or shows an 'off' position
• Zone of Ambiguity: Center of TO and FROM
• Reverse Sensing: Pilot error

Distance Measuring Equipment (DME)

• DME is a navigation beacon, coupled with a VOR beacon
• DMEs allow aircraft to measure their position relative to a beacon
• Aircraft send out a signal which is sent back after a fixed delay by the DME ground equipment
• Aircraft compute the distance to the beacon from the delay of the signal perceived by the aircraft's DME equipment using the speed of light
• DMEs calculate continuous slant range distance-from-station readout
• DMEs measure time-lapse of a signal transmitted by the aircraft to the station and responded back
• DMEs can also provide groundspeed and time-to-station readouts by differentiation

VOR vs DME

• VOR provides the ability to capture and track any radial, but it only provides direction
• More information is needed in order to determine actual location
• Can use information from 2 VORs and see where the radials intersect on a map to determine location
• VOR is passive, no input required from the plane
• DME, Distance Measuring Equipment is required for operation above FL240, Ultra-high frequency
• DME is active, requires transmitter and receiver at each end (Plane and DME)
• Plane must send a signal to DME for it to activate

Marker Beacons

• Marker beacons are vertically broadcast radio signals
• Marker beacons indicate distance from the runway
• The outer marker are more sensitive (narrower broadcast vertical cone) closer to the runway

Outer Marker

• Identifies the final approach fix (FAF)
• Situated on the same course/track as the localizer and the runway centerline, four to seven nautical miles before the runway threshold
• Located about 1 NM (1.85 km) inside the point where the glideslope intercepts the intermediate altitude
• Transmits a 400 Hz tone signal
• The valid signal area is a 2,400 ft (730m) × 4,200 ft (1,280 m) ellipse measured 1,000 ft (300 m) above the antenna
• Markers beacon receiver detects the signal as aircraft passes over the marker antenna

Middle Marker

• A middle marker works on the same principle as an outer marker
• It is normally positioned 0.5 to 0.8 nautical miles (1 km) before the runway threshold
• The receiver's amber middle marker light starts blinking as the aircraft is above the middle marker
• A repeating pattern of audible Morse code-like dot-dashes with frequency of 1,300 Hz in the headset can be heard
• This alerts the pilot that CAT I missed approach point (typically 200 feet (60 m) above ground level on the glide slope)

Inner Marker

• Located at the beginning (threshold) of the runway on some ILS approach systems (usually Category II and III)
• Has decision heights of less than 200 feet (60 m) AGL
• Triggers a flashing white light on the marker beacon receiver and audio tone 'dots' at a frequency of 3,000 Hz in the headset